Susceptibility of Microplitis croceipes and Cardiochiles nigriceps (Hymenoptera: Braconidae) to Field Rates of Selected Cotton Insecticides¹

Microplitis croceipes (Cresson) and Cardiochiles nigriceps Vierick, parasitoids of Heliothis virescens (F.), were treated topically with field rates of 14 formulated insecticides commonly used in cotton insect control. The 14 insecticides were oxamyl, thiodicarb, endosulfan, acephate, azinphosmethyl, chlorpyrifos, dicrotophos, dimethoate, methyl parathion, profenofos, bifenthrin, cyhalothrin, cyfluthrin, and cypermethrin. With the exception of thiodicarb, all insecticides were extremely toxic to M. croceipes, causing 100% mortality of adult wasps. Treatment with thiodicarb resulted in high survival of adults for each parasitoid species. Acephate was extremely toxic to M. croceipes, but relatively non-toxic to C. nigriceps. Mortality also was lower for C. nigriceps females than for C. nigriceps males and M. croceipes for both sexes when wasps were treated with oxamyl. Nine of the 14 insecticides tested were extremely toxic to C. nigriceps, causing 100% mortality of adult wasps. Treatment with 5 insecticides - thiodicarb, acephate, oxamyl, azinphosmethyl, and cypermethrin - resulted in higher survival for C. nigriceps adults than was obtained for the other nine insecticide treatments. For both male and female C. nigriceps, thiodicarb and acephate were less toxic than the other three insecticides. Generally, these five insecticides were less toxic to females than males. An exception was the lower mortality of male C. nigriceps versus females of this species for treatment with acephate. Of the three insecticides commonly used for boll weevil control (oxamyl, azinphosmethyl, and methyl parathion), oxamyl was the least toxic to C. nigriceps females. Cypermethrin was less toxic to C. nigriceps females than the other three pyrethroids tested. Selective use of insecticides which permit higher parasitoid survival could facilitate conservation of these native biological control agents.